Adjusting the density of a liquid in a predictably repeatable fashion is a desired feature in many fields of manufacturing. Although this adjusting feature is not limited to the manufacture of foods, this adjustment of density is critically useful in the manufacture of foods, especially a food which is customarily sold and consumed while in a frozen state. Typical of such a frozen, consumable product is ice cream and similar products. The control of a fluid addition to the liquid is required in several processes to create a final liquid characteristic or hardenable liquid characteristic, which generally has a lesser density than the original fluid stream.
Foods, which are normally consumed in a frozen state, have a number of critical factors which must be met in order to make a suitable food. Such a food can become inedible due to high bite resistance. By high bite resistance is meant that a person cannot break off a piece of the product by biting the product.
In addition to producing a product with proper bite resistance, control of product composition and melt characteristics can result by establishing and maintaining consistent quality standards. But frozen products can vary widely in mix composition and freezing requirements. This problem leads to a need for repeatable mix ingredient assembly and control of variables of the freezing process to meet the individual product manufacturing criteria.
Conventional manufacturing plants must solve these seemingly contradictory problems. To do that, a plant needs to alter the process variables over a wide range, especially the freezing temperature and amount of air injected. Water ices and sherbets require substantially less air than bulk ice creams, while at the same time often having higher freezing temperatures.
Operating manufacturing plants require accurate and repeatable methods to alter and control the variables within their processes. This then creates a market for equipment and controls that accurately and repeatably address these methods. No apparatus exists to address these problems and methods.
A variety of approaches may be used to control this density factor. However, none of the procedures known in the prior art provide a method or apparatus capable of a controlled, constant testing or metering of density, in order to provide a reliably uniform product.
One method injects air into the liquid. The air volume is, however, dependant on the rate of the flowing liquid. There is no way of controlling the amount of air, while having the volume of air dependant on the flowing liquid.
As a recognition of the desire to have a sometimes variable amount of fluid added to the liquid, it is known to have a variable port for permitting the entry of the fluid such as air or other liquid into the steam. However, the rate of the gas addition is varied by outside intervention is not controlled based on readings from the flow of the liquid. This factor prevents the accurate control of density.
It is also known to determine the relative air or gas content of a product by comparing relative volumes in a sampling chamber with a compression system. The sample is compressed by a series of movable pistons. While this method can be used as a means of measuring the relative volume differences in the two samples, it cannot control the rate of gas addition nor can it operate as a quality control to continuously adjust the gas addition rate and achieve the desired density.
Another method involves using a volumetric, electromagnetic, flow meter in line with a control circuit to control addition of air to a liquid especially with using air mass flow control. This approach is based on a volumetric flow metering device and cannot compensate for variations in incoming fluid density by volumetric metering means. The liquid air ratio is controlled on a direct volume of liquid to volume of gas basis. This process cannot yield a liquid of desired density since temperature and mass of the liquid are not controlled.
Still another method of mixing a fluid with a liquid includes mixing a liquid component with another liquid component based on the volume measurements of a measuring device. With the adding of the liquid, this method permits the adding of one liquid to another to adjust the density of the resulting mixture. However, it still provides no reliable manner of determining and sustaining a desired density of the final liquid.
It is possible to add gas to a liquid stream based on maintaining a gas to liquid ratio by means of pressurizing the gas liquid mixture. The purpose of this idea is to create a carbonated beverage which contains gas to an approximate volume. The density of the resulting liquid may vary and does not create a basis for determining the amount of gas which is incorporated into the liquid or beverage, while achieving a desired density.
Furthermore, it is known to introduce air into the freezing chamber based upon a monitoring system for the loading of the dasher motor to maintain a constant desired product density. This continuous process alters the air intake by the indirect measurement means and cannot qualify as a control or quantifying device to a desired product density. Only external sampling means can be used to determine appropriate mechanism.
Thus, many problems still exist with adjusting the density of product by mixing and liquid and a fluid. This is especially true because no known apparatus uses a primary liquid metering device in combination with a computer controlled constant test of density.
The concept of overrun control requires a review of frozen product manufacturing and an understanding that without the injection of air or other gas, most frozen products become inedible due to high bite resistance. In other words, a person cannot break off a piece of the product by biting the product.
Freezing a dairy or food product often means causing a phase change in a solution, which may contain added solids or lipids or both. If water only is frozen, the resulting ice compound is difficult, if not impossible, to bite through or chew. Addition of solids; such as milk powders, sweeteners, or a similar food item used alone or in conjunction with lipids such as butterfat or vegetable oils; will cause the overall freezing point to be depressed below that of water. Depending on the composition of the mix, the normal freezing point may be depressed ten (10.degree. F.) Fahrenheit degrees (five (5.degree. C.) centigrade degrees) or more.
As temperatures are lowered during the freezing process the water begins to crystalize and bind the solids. Following homogenization, the fats and oils will become dispersed throughout the solution and will also become bound within the crystallization complex. This crystalline complex, like ice, is not easily consumed due to the high density of the resulting product.
If air or other edible gas mixture or a fluid is injected and evenly dispersed throughout the fluid mix during the freezing process small air cells result and the overall structure of the frozen product becomes very different. Each air cell tends to retain its structure surrounded by solids, fat globules, and water crystals. Variations in fat content, solids content, freezing temperature, freezing equipment, amount of air injected, and effectiveness of whipping the air/mix solution all have extremely high impact toward the final frozen product consistency and degree of consumer acceptance.
Overrun as a measurable variable in the manufacturing process is defined as the volume of product (such as ice cream) which results from the volume of mix frozen. This is often stated as a percentage and makes the assumption that the final product volume is greater than the volume of mix to give a positive percentage.
As stated previously, the variable amount of air depends not only on processing methods and mix composition, but also on the extent that consumer acceptance criteria; such as body, texture, bite resistance, taste, and appearance; are met. These factors along with legal standards of identity, addition of injected fruits or nuts, type of packaging, and type of marketing all contribute to establishment of overrun criteria for a given product.
A method for calculation of overrun on a volume basis is: ##EQU1##
Alternatively overrun (for a product such as ice cream) may be calculated on a weight basis as: ##EQU2##
The former method utilizing a volume based calculation is susceptible to interference from both formulation and temperature induced density variations. If the calculation is based on the volumetric measurement of mix and a volumetric determination of actual frozen product produced, then no input is made to reference a standard temperature of pressure and the resultant percentage may be affected by differences in the actual mixes being used. Present freezer equipment manufacturers are utilizing an electromagnetic flowmeter for volumetric measurement of fluid mix entering the freezer systems.
This method then becomes the basis for the overrun control and, as noted, cannot compensate for density variations in the fluid mix. Often the process methods will cause partially aerated and partially frozen product to be returned to the source tank which supplies the freezer in a way so as to prevent large losses of valuable product. This is especially prevalent during system start-up while temperatures are being adjusted and during shutdown or product change over. The result of this practice is to affect the ideal density of the source product and add air based upon volume which is not properly measured since the electromagnetic flowmeter provides an output of volume only, which does not compensate for density variation.